US2191057A - Facsimile transmitting and receiving system - Google Patents

Description

Feb. 20, 1940. DURKEE 2,191,057

FACSIMILE TRANSMITTING AND RECEIVING SYSTEM Filed July 25, 1938 2 Sheets-Sheet 1 INVENTOR.

Jame/0P3 BY Feb. 20, 1940. J. b. DURKEE 2,191,057

' FACSIMILE TRANSMITTING AND RECEIVING, SYSTEM Filed July 25, 1958 2 Sheets-Sheet 2 m T INVENTOR. L

Patented Feb. 20, 1940 f I" i UNITED STATES PATENT OFFICE FACSIMILE TRANSMITTING AND RECEIV- ING SYSTEM l James D. Durkee, Bartlesville, Okla, assignor to Phillips Petroleum Company, Bartlesville, kla., a corporation of Delawar e Application July 25, 1938, Serial No. 221,223

9 Claims. (Cl. 178-7.1)

My invention relates broadly to the transmisopen to frequencies at the one extremity of the sion and reproduction of facsimile pictures and band of frequencies, and substantially closed to more particularly to a frequency modulated audio frequencies at the other end of the band.

, frequency system. Other and further objects of my invention re- This application is a continuation-in-part of side in the circuits and arrangements hereinafter 5 my'application Serial Number 37,578, filed Augmore fully set forth with reference to the accomust 23, 1935, for Facsimile transmitting and repanying drawings, in which: Figure 1 is a scheceiving system. matic diagram of the circuit connections in the In picture transmitting systems wherein a ratransmitting system of my invention; Fig. 2 is a 0 dio frequency carrier current is modulated in similar schematic diagram of the circuit connecintensity directly by the varying current from a tions in the receiving system of my invention; light sensitive cell, the varying tones in the picand Fig. 3 is a schematic circuit diagram of a ture being transmitted are registered too sharply modified form of the transmitter shown in Fig. 1. in the reproduced image, resulting in a facsimile The system of my invention involves frequency of inferior quality. modulation within a relatively narrow audio band 15 One of the objects of my invention is to proof a beat frequency resulting from the coaction vide a system of facsimile reproduction in which f a p a ty of high frequency OSCiIIotOI'S- e the lights and shadows in the original picture f q n y odu t d av s then employed, in are accurately reproduced, the preferred form of my invention, to modulate Another object of my invention is to provide a a radiofrequency carrier current whereby the 2 modulating system wherein impact excitations of modulations may be transmitted y Space radio the carrier due to sharp changes in the intensity or line wire. At the receiver, the radio frequency of the light focused on the photo-cell are elimicarrier current is rectified, and the detected varynated from the modulator output, and the signal ing audi f equ n y rr s are p y t current caused to vary directly as the intensity of energize a li ht r e in intensity varying as 2 the light varies the modulations of the audio frequency.

Still another object of my invention is to pro- The system of my invention operates to transvide means for modulating a radio frequency carmit the light variations in successive minute porrier current by means of an audio frequency wave, tions of the subj c picture A Scanning System the frequency of which is made to vary in aeat the transmitter and a synchronized system at 30 cordance with the light intensity of successive the receiver are accordingly required. These points in a picture to be transmitted. m y be f ny of the yp s wn n he A further object of my invention is to provide the system f my inv n n e n onc n d prian intermediate audio frequency oscillator the marily With e transmission of the Varying Color frequency of which is modulated in accordance tones in the subject p u with the variations in light intensity in a picture Referring to the drawings in more detail, Fig. 1 being scanned; the modulated audio frequency illustrates 1Jhe transmitting arrangement of my being employed to modulate the intensity of a invention. Reference character I indicates a radio frequency carrier current for transmitting constant light source focused by lens 2 on the by space radio or line wire the subject picture. l ght sensitive cell 3. A drum 4, carrying the film 40 A still further object of my invention is to pro- 5 which bears the picture to be transmitted is vide an audio beat frequency oscillator, the freoved by u a mechanical means, including quency of which is modulated by varying the a motor 5, so that the light beam from the source frequency of one of the component frequencies, 1 passesthreugh Successive minute p o s of to modulate a radio frequency carrier current. h fi being V d n t s y with the den- 45 Still another object 'of my invention is to prosity of the film a d energizing the light Sensitive vide a translating system for detecting the frecell 3 according yquency modulated audio wave and employing the The Cell 3 s Connected in lJhe pu c rcuit modulations thereof to actuate a recording means f an e ron tu e a plifier stage 1, the output by changing the intensity of a light source. of which is fed to an electromagnetic device 50 A still further object of my invention is to p sing a magnetic core structure 8 and an provide a filter device in the translating system armature 9, 1 W ch is Wound a coil l0 conresponsive in uniformly varying effect over the nected in the output circuit of the amplifier 1. band of frequencies over which the frequency The armature 9 is mechanically connected by modulation extends, the filter being effectively means of shaft I 2 with the movable section Ma 55 of a Variable condenser It which is connected in the circuit of a high frequency oscillator l5 and operable to vary the frequency of the oscillations generated therein.

A similar high frequency oscillator 16 has its output coupled with the output of the oscillator i5 in the combining circuit ll. Oscillators l5 and it are preferably normally adjusted to operate at the same frequency and to produce a zero beat in the combining circuit i'l. Oscillators l5 and iii may, however, be adjusted so as normally to produce any desired fundamental beat frequency. The combining circuit l1 includes the secondaries of coupling transformers H and 22, the primaries of which are connected in the output circuitsof the oscillators I5 and I6, respectively. As indicated in Figs. 1 and 3, these transformers, carrying high frequency currents from the oscillators, have a substantial amount of iron in the cores flu, and 22a, saturable at thehigh frequencies of the oscillators so that the transformers have non-linear frequency responsive characteristics. Connected in the series circuit l'l, the secondaries of these transformers H and 22 comprise a combination having a non-linear characteristic, wherein the output currents of the oscillators l5 and it beat and result in a zero or low frequency beat wave to which the circuit H is linearly responsive. As the condenser M connected in circuit with oscillator I5 is varied by the electromagnetic means controlled by the variations of light on the cell 3, the frequency of the oscillations produced in oscillator I5 is modulated according to the light variations on the cell 3. The beat frequency, which is of audible magnitude, appearing in the combining circuit i'l likewise varies in accordance with the fluctuations in intensity of the light focused on the cell 3.

The combining circuit H is connected with a filter circuit 58 having the dual function of first excluding the higher fundamental harmonic frequencies of the component oscillations issuing from the oscillators it, It, and second of passing currents of beat frequency, within the band covered by the modulations introduced by the condenser it, in varying intensities depending upon the instantaneous frequency of the wave. That is, the frequencies at one end of the band will be passed Without diminution of the intensity of the current, while the frequencies at the other end of the band will be substantially suppressed and currents at those frequencies correspondingly diminshed, the current passed by the filter l8 decreasing uniformly with proportionate changes in the frequency thereof. In other words, the frequency modulations and the current passed by the filter vary in a straight line relation.

The filter i8 is coupled with an electron tubeamplifier it so that the voltage on the grid thereof is directly proportional to the magnitude of the beat frequency and, accordingly, to the intensity of the light on the cell 3. The output of amplifier i9 is employed to modulate a high frequency carrier wave produced in an oscillator at 21], the modulation consisting of. the beat frequency wave which varies not only in frequency but also in magnitude with the light intensity signal. The modulated carrier is fed to a radiating system including antenna 2i and ground 23.

At the receiver the modulated radio frequency carrier current is intercepted in the usual manner by tuningto the frequency of the carrier current, by means of the resonant circuit 24, Fig.

2, and rectified in the usual manner in a detector 25. The audio frequency modulations thus detected are amplified in the electron tube stage 26 and fed into an audio frequency band pass filter 2? which transmits currents of all fre quencies within its range substantially uniformly. Further amplification may be obtained in the electron tube stage 3? from which the energy is fed to a source of light, such as a neon lamp, at 28, the intensity of the light produced thereby varying with the magnitude of the applied voltage. The light is focused by lens Eli upon the light sensitive film (iii which is fixed on a drum l driven by synchronized scanning means including motor 3.

Assuming that the beat note produced at the transmitter in the combining circuit ll, Fig. l, Varies between 500 and 1000 cycles, a plurality of beat frequency oscillators may be connected for multiplex operation, each employing a range of frequencies independent'from the others. A corresponding plurality of filter systems Z'l may be provided at the receiver, each operative over a predetermined band in cooperation with the ranges of heat frequencies selected at the transmitters.

Fig. 3 shows a modified form of transmitter employing electrostatic means for varying the frequency of the component oscillator H5, in place of the electromagnetic control means and a variable condenser shown in Fig. l. The electro static device 3i may be the operative unit of a condenser microphone, in which case the electron tube in amplifier stage i should have a high impedance output circuit. The plate voltage of the tube acts as a biasing potential on the condenser plates, and variations in the instantaneous voltage across a resistor 32 in the output circuit of the tube due to the variations in light intensity on the photoelectric cell 3 will be effective directly as changes in capacity. The condenser device 3| is coupled to the circuit of the high frequency oscillator it through condensers 3t and 35, and connected with the low frequency amplifier stage i by choke coil 35 in order to confine the high frequency currents from the oscillator l5 to the condenser plates. The condenser device 3| will thus be acted upon by the voltages across the resistor 32, and function, in place of the variable condenser it shown in Fig. i, to modulate the frequency of the oscillator iii, A wider frequency band will be required using the circuit of Fig. 3 than is possible with that of Fig. 1, as the diaphragm of a condenser microphone will respond to frequencies as high as 10,300 cycles per second, but greater sharpness of definition in the facsimile willbe assured,

A further modification of Fig. 1 shown in Fig; 3 is the provision of an electron tube stage at 38 operative as a detector wherein the oscillations from oscillators i5 and i6 beat. The outputs of the oscillators I5 and itv are coupled by conventional transformer means to the circuit at IT connected with the input of detector 38. The output of the detector is applied to the filter I8,

as is the beat frequency output of the combining circuit l! in Fig. l, and the filter it functions as hereinbefore described to pass current in proportion to the beat frequency. The remainder of the circuit is similar to that of Fig. l. The electron tube detector stage 38 may be provided in the arrangement of Fig. 1 in lieu of the nonlinear transformer devices comprising the combining circuit IT to effect the same results, if desired. It will be noted,however, that the filter s and itstwo-fold function are featured in both circuitsand is an essential element of the system of my invention;

The transmission method of my invention prosults in no impact excitations such as result from direct'modulation of the carrier. Freed from the impact excitations which extend over a relatively broad space in the frequency spectrum, the-system of my invention is capable of transmitting a number of pictures in the band width heretofore required for the transmission of a single picture.

While I have described my invention in certain of its preferred embodiments, I desire that it be understood that modifications may be made by those skilled in the art, and that no limitations upon my invention are intended other than may be imposed by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In an image transmitting system, the method of transmitting variations of light intensity which comprises generating a beat frequency wave by the coaction of two independent oscillations, modulating the frequency of one of the independent oscillations and thereby modulating the beat frequency, regulating the amplitude of the beat frequency wave in accordance with the frequency of the same, generating a radio frequency carrier current, modulating the radio frequency carrier current by the beat frequency wave, detecting the modulated radio frequency carrier to reestablish the modulated beat frequency, employing the modulated beat frequency to vary the intensity of a light beam in accordance with the amplitude of the beat frequency 1 wave, and recording the varying intensities of the light beam.

2.'In an image transmitting system of the type described, the method of modulating a radio frequency carrier current which comprises initially modulating the frequency of an audio wave resulting from the coaction of a pair of high frequency oscillations, regulating the amplitude of the audio wave in accordance with the frequency thereof, and subsequently employing the audio wave to modulate a radio frequency carrier current.

3. In an image transmitting system of the type described, the method of modulating a radio frequen-cy carrier current which comprises, generating a beat frequency wave by the coaction of two independent oscillations, modulating the frequency of one of the independent oscillations in accordance with color tone variation of a picture or object and therebymodulating the beat frequency, regulating the amplitude of the beat frequency wave in accordance with the frequency thereof, and employing the beat frequency wave to modulate a radio frequency carrier current.

4. In an image transmitting system, means for transmitting variations of light intensity which include a beat frequency oscillator comprising a pair of individual oscillation generators, and means for combining the outputs of said generators to produce an oscillation of beat frequency; means connected in one of said oscillation generators and controlled in accordance with color tone of a picture or object for varying the frequency of said one oscillation generator, the frequency of said! beat frequency oscillation being modulated accordingly; and an audio frequency filter system connected with said combining means and adapted to pass current in proportion to its frequency within the range of said filter 1 system. I

5. In an image transmitting system, a source of energy comprising separate oscillator circuits, means for modulating the frequency of. one of said oscillator circuits in accordance with the lights and shades in the image transmitted, the frequency of the other of said oscillator circuits being constant, transformer means in the output of each of said oscillator circuits and having nonlinear frequency responsive characteristicsin the range of frequencies of said oscillator circuits,

, said transformer means having secondary winda relatively low value and variable in accordance with the initial modulation of the first said osclllator circuit, a filter system connected with said combining circuit and operative to pass current of the beat frequency in proportion to its frequency, and means for modulating a carrier current in accordance with the output, of said filter system.

6. In an image transmitting system, means for modulating a carrier current in accordance with the lights and shades in the image transmitted, which include a beat frequency circuit fed by separate oscillator circuits, the frequency of one of said circuits being varied by the light intensity signal while the frequency of the other of said circuits is constant, said beat frequency circuit comprising the secondary windings of separate transformer means coupled with said oscillator circuits and having non-linear frequency responsive characteristics in the range of frequencies of said oscillator circuits, and a filter system operative to pass currents of the modulation beat frequency issuing from said beat frequency circuit in proportion to the frequency thereof.

'7. In an image transmitting system, a beat frequency oscillator constituting means for relieving a carrier current of abrupt changes in modulation due to impact excitation of a photo-cell by sharp changes in thelight intensity signal thereon, said beat frequency oscillator comprising separate oscillator circuits, the frequency of one of said circuits being varied by the light intensity signal While the frequency of the other of said circuits is constant, and transformer means connected in the output of each of said oscillator circuits and having non-linear frequency responsive characteristics in the range of frequencies of said oscillator circuits, said transformer means having secondary windings connected in series combining circuit.

l 8. In an image transmitting system, a beat frequency oscillator interposed between photo-electric modulating means and a carrier modulating circuit, said beat frequency oscillator including a combining circuit inductively coupled with separate oscillator circuits and having a non-linear frequency responsive characteristic in the range of frequencies of said oscillator circuits and a linear frequency responsive characteristic inthe range of the beat frequencies, the photo-electric modulating means being arranged to modulate the frequency of one of said oscillator circuits in accordance with color tone variation of a picture or object, and means connected with said combining circuit for translating variations in the beat frequency into current variations for said carrier modulating circuit.

9. In an image transmitting system, photoelectric scanning means, a source of alternating current controlled in frequency by said scanning means in accordance with light intensity in the object scanned, and means for regulating the amplitude of the alternating current from said source in accordance with the frequency thereof, said current of variable frequency being employed to modulate a carrier Wave and the amplitude variations of said current being adapted to control the intensity of a light beam for producing 10 an image of the object scanned.

JAMES D. DURKEE.

. I CERTIFICATE OF CORRECTION. Patent No. 2,191,057. February 20, 1 1p.

JAMES D. DURKEE It 15 hereby certified that error appears .in the printed apecificaticn of the above numbered patent requiring correction as follows Page 5, first column; line 71+, claim L after the word "ton'e'! insert variation; and that the said Letters Patent should be read'with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed: and sealed this 2nd day of April, A. D. 191 0.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

Images